Pressure switch with linearly movable can-actuating means and overstress-responsive safety valves

ABSTRACT

A pneumatically operated master controller switch device embodies therein a pair of snap-acting switches for effecting respectively energization and deenergization of a pair of magnet valve devices via a corresponding one of a pair of wires accordingly as one or the other of the switch devices is actuated by a minimum of movement of a movable abutment in response to variations in the fluid pressure on one side thereof with respect to the fluid pressure present on the other side. Safety valve means are positioned at each end of movement of the moveable abutment, and are actuated to restore a pressure balance and return the abutment to the neutral position, thus preventing damage due to overstress.

United States Patent [72] Inventors William B- Jelfrey 2,982,830 5/1961 Schaefer et al. ZOO/83(5) Irwin; 2,991,343 7/1961 Norden 200/I53(.l2) R a Frill, Pittsburgh, a- 3,1 14,387 12/1963 Barkan et al..... 137/494 [21] Appl. No. 741,369 3,148,364 9/1964 Engels et a1 ZOO/83X [22] Filed July 1,1968 3,192,349 6/1965 I-Iorbert,Jr.. 200/153(.12) [45] Patented Apr. 6,1971 3,341,673 9/1967 Arnold 200/83 [73] Assignee Westinghouse Air Brake Company FOREIGN PATENTS 1,069,746 11/1959 Germany 200/153 .12

Primary Examiner-Robert K. Schaefer [54] PRESSURE SWITCH WITH LINEARLY MOVABLE Assistant Examiner Roben vanderhye CAN-ACTUATING MEANS AND OVERSTRESS' AttorneysAdelbert A. Steinmiller and Ralph W. Mclntire, RESPONSIVE SAFETY VALVES J 2 Claims, 1 Drawing Fig.

[52] US. Cl ZOO/81.4,

ZOO/83 ZOO/153 9 3 ABSTRACT: A pneumatically operated master controller [5 1] Int. Cl. H01h /34 Switch device embodies therein a pailf Snapacting Switches 35/24 for effecting respectively energization and deenergization of a Field of Search 303/3, 15, pair of magnet va|ve devices via a corresponding one f a pair 16; ZOO/8391, 83-1, 8221 15319 of wires accordingly as one or the other of the switch devices 4 83; 137/100 101,494; is actuated by a minimum of movement of a movable abut- 251/82 ment in response to variations in the fluid pressure on one side 56 R f d thereof with respect to the fluid pressure present on the other 1 e fences l e side. Safety valve means are positioned at each end of move- UNITED STATES PATENTS ment of the moveable abutment, and are actuated to restore a 2,475,069 7/1949 Wood... 200/83(.32)X pressure balance and return the abutment to the neutral posi- 2,820,l 17 I/ 1958 Waite 200/83( .34) tion, thus preventing damage due to overstress.

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68 5 54 I, r 69 63 1 iw 37 s 34 as 7 1 3? 86 ea 1 9a LL/y m u 92 1 I I: \3? o I 61 50 7 41 j 6 a1 a5 8 I I I 1 e I 1 2 1 1 g; \57 55 4344 m e9 1H 56 /49 73 .1. 1H1 -72, 78 1 9a 1 -112 I 1 1 i 104 1 fl 1" 3a 0a X153 ee @1 25a 5B 3039 \x o5 W 2e b 27 58 3O PRESSURE SWITCH WITH LINEARLY MOVABLE CAN- ACTUATING MEANS AND OVERSTRESS-RESPONSIVE SAFETY VALVES BACKGROUND OF THE INVENTION Electropneumatic brake systems comprising pneumatically operated master controller switch devices for controlling the electrical train wire circuits of electromagnet valves on the cars in a train so as to effect variations of pressure in a train pipe, such as a train brake pipe, have been known in the railway braking art for many years. US. Pat. 1,875,738 issued Jun. 6, 19 l 6, to Walter V. Turner and assigned to the assignee of the present application discloses such a system. However,

. this Turner patent merely discloses an electromagnet valve for releasing fluid under pressure from a train brake pipe without any electromagnet valve means for supplying fluid under pressure to the brake pipe for effecting the charging thereof to effeet a brake release. Moreover, there are many forms and designs of fluid-pressure-operated master controller switch devices known in the braking art. However, it has been found that in actual practice these fluid-pressure-operated master controller switch devices 'tend to be sluggish in operation which causes undesirable arcing at and consequent pitting of their electrical contacts. This, in turn, has resulted in chattering of the magnet valves thereby causing rapid wear of the respective valves and their corresponding valve seats.

The above-mentioned sluggish operation of fluid-pressureoperated master controller switch devices results in overcasting of pressure changes and consequent pumping action until a balanced pressure condition is achieved. More specifically, the delayed opening of the contacts causes the reduction of the pressure in the train-brake pipe and on one side of an abutment that operates the switch device to exceed, that is overcast, the reduction of the pressure previously manually effected, by operation of the brake valve device, in the equalizing reservoir and on the opposite side of this abutment. Such undesired overcasting thereafter causes undesired reclosing of the release contacts to effect energization of the release electromagnet valves which in turn cause the supply of fluid under pressure to the train brake pipe. This buildup of pressure in the train brake pipe results in an undesired partial release of the brakes and also in an increase in the fluid pressure acting on the one side of the abutment thereby effecting reclosing of the application contacts whereupon the above-described cycle is repeated. This undesired cycling is termed pumping. Furthermore, brake pipe leakage reduces the fluid pressure on the one side of the abutment which in turn effects respective operation of the master controller switch devices to maintain the desired pressure.

Accordingly, it is the general purpose of this invention to provide a fluid-pressure-operated master controller switch device for controlling respectively the energization and the deenergization of an application train wire and a release train wire extending through the cars in the train in a manner to minimize cycling or pumping action of the controller.

SUMMARY OF THE INVENTION According to the present invention, a pair of snap-acting switches are embodied in a master controller switch device so that one or the other is actuated to its closed position by a minimum of movement of a movable abutment in response to variation in pressure effective on one side thereof with respect to the pressure on the other.

The master controller switch device constituting the present invention is rendered faiLsafe in that it embodies therein a pair of vent valves disposed on the respective opposite sides of the abutment and is operative responsively to a chosen degree of deflection of the abutment in one direction or in an opposite direction, occurring only upon failure of a corresponding one of the pair of snap-acting switch devices or a circuit controlled thereby, to vent fluid under pressure respectively from the side of the abutment subject to the higher pressure to the side subject to the lower pressure thereby restoring a balance of the fluid pressure forces acting on the abutment.

In the drawing, the single FIGURE is a vertical cross-sectional view, showing details of a pneumatically operated master controller self-lapping switch device.

The pneumatically operated master controller self-lapping switch device 9 shown in the drawing comprises a sectionalized casing constituting a pair of easing sections 25 and 26 between which is clamped the outer periphery of a diaphragm 27 by a plurality of cap screws 25a the heads of only two of which appear.

The diaphragm 27 cooperates with the casing sections 25 and 26 to form within the master controller self-lapping switch device 9 and on the respective opposite sides of the diaphragm 27 a pair of chambers 28 and 29. Opening into the chamber 28 is a passageway 30 extending through the casing section 25 to the exterior thereof to which a correspondingly numbered pipe may be connected for supplying fluid under pressure to chamber 28.

Opening into the chamber 29 is a passageway 33 extending through the casing section 26 to the exterior thereof to which a correspondingly numbered pipe may be connected for supplying fluid under pressure to the chamber 29.

The casing section 26 is provided with a central bore 34 which opens at one end into the chamber 29 and at the other end to atmosphere. A wear bushing 35 is press-fitted into the bore 34 and slidably mounted in this bushing 35 is a stem 36 that extends into the chamber 29. That portion of the stem 36 disposed within the chamber 29 is provided with a collar 37 that on its left-hand side forms a shoulder against which rests a diaphragm follower 38 that is operatively connected to the center of the diaphragm 27 by means such as a diaphragm follower plate 39 and a nut 40 that has screw-threaded engagement with screws threads formed on a portion of the stem 36 intermediate the collar 37 and the left-hand end thereof which portion passes through corresponding smooth bores in the diaphragm follower 38 and diaphragm follower plate 39. This portion of the stem 36 is also provided with a peripheral annular groove in which is disposed an O-ring 41 to prevent leakage of fluid under pressure between the periphery of the stem 36 and the wall of the bore in the diaphragm follower 38 and also between the chambers 28 and 29.

The casing section 25 is provided with a bore 42 that is coaxial with the bore 34 and opens at its respective opposite ends into the chamber 28 and a first coaxial counterbore 43 in this casing section. A wear bushing 44 is press-fitted into the bore 42 and slidably mounted in this bushing 44 is a stem 45 the right-hand end of which is provided with a bottomed bore 46 that has disposed therein the left-hand end of the stem 36 which is operatively connected to the stem 45 by a pin 47 extending through a bore 48 formed in the stem 36 adjacent its left-hand end and a coaxial bore 49 of the same diameter pro vided in the stem 45. Formed on that portion of the stem 45 extending through the bushing 44 is peripheral annular groove in which is disposed an O-ring 50 to prevent leakage of fluid under pressure between the chamber 28 and the counterbore 43 into which opens one end of a passageway 51 formed in the casing section 25 and extending therethrough to the exterior thereof to which a correspondingly numbered pipe may be connected for supplying fluid under pressure to the counterbore 43.

As shown in the FIGURE, the left-hand end of the counterbore 43 in the casing section 25 opens into a coaxial second counterbore 54 of larger diameter provided in this casing section. An annular member 55 is press-fitted into the left-hand end of the counterbore 43 and is provided on its left-hand end with an annular valve seat 56 against which normally is biased a disc-type valve 57 disposed in the counterbore 54. Opening into the counterbore 54 is one end of a passageway 58 formed in the casing section 25 and extending therethrough to the exterior thereof to which a correspondingly numbered pipe may be connected through which pipe fluid under pressure may be supplied to a device to be operated thereby.

The left-hand end of the counterbore 54 is closed by a cover member 59 which is secured to the casing section 25 by a plurality of cap screws 60 one of which appears in the FIGURE.

The cover member 59 is provided with a bore 61 and a coaxial counterbore 62 that are coaxial with the bore 42 in the casing section 25. A wear bushing 63 is press-fitted into the counterbore 62 and a valve guide member 64 is slidably mounted in this bushing 63. The right-hand end of the guide member 64 is provided with a bottomed bore 65 in which is received the left-hand end of a stem 66 integral with the disc-type valve 57. This stem 66 is operatively connected to the valve guide member 64 by a pin 57 in the same manner as the left-hand end of the stem 36 is connected to the stem 45.

The valve guide member 64 is provided with a peripheral annular groove in which is disposed an O-ring 68 that forms a seal with the wall surface of the bushing 63 to prevent leakage of fluid under pressure from the interior of the counterbore 54 to atmosphere. interposed between the cover member 59 and the valve guide member 64 is a spring 69 which is effective via the pin 67 and stem 66 to normally bias the valve 57 against its seat 56 to close communication between the passageways 58 and 51 except when the valve 57 is unseated in a manner hereinafter described.

The diaphragm 27 is normally biased to the position shown in the FIGURE by a pair 'of identical springs 70 and 7] respectively disposed on the opposite sides thereof. The spring 70 is arranged in surrounding relation to the stem 36 and is interposed between the diaphragm follower plate 39 and an outturned flange that is formed at one end of an annular spring seat 72 that is disposed in a counterbore 73 formed in the easing section 25 and coaxial with the bore 42 therein. This spring seat 72 has formed at its opposite end an inturned flange which, while the diaphragm 27 is biased by the springs 70 and 71 to the position shown in the FIGURE, abuts the right-hand end of the stem 45.

Likewise, the spring 71 is arranged in surrounding relation to the stem 36 and is interposed between the diaphragm follower 38 and an out-turned flange that is formed at one end of a second annular spring seat 74 that is disposed in a counterbore 75 formed in the casing section 26 and coaxial with the bore 34 therein. This spring seat 74 has formed at-its opposite end an inturned flange which, while the diaphragm 27 is biased to the position shown in the FIGURE, abuts a snap ring 76 carried by the stem 36 on the right-hand side of the collar 37 and spaced therefrom.

As shown in the FIGURE, one leg of an angle bracket 77 is secured to the right-hand end of the casing section 26 by a plurality of screws 78 the heads of two of which are shown in the FIGURE. The one leg of the angle bracket 77 is provided with a bore 79 through which extends the right-hand end of the hereinbefore-mentioned stem 36. This right-hand end of the stem 36 is provided with a bottomed bore 80 in which is received a stem 81 of substantial smaller diameter than the stem 36 and formed on the left-hand end of a cylindrical switch-operating member 82. This operating member 82 is secured to the stem 36 for movement therewith by a pin 83 that extends through a bore 85 formed in the stem 81 and coaxial bores in the stem 36. Intermediate its ends the switchoperating member 82 has formed thereon an elongated peripheral annular groove 86 the opposite ends of which are inclined at an angle of, for example, 30 with the horizontal.

Secured to the other leg of the angle bracket 77 by any suitable means (not shown) in spaced-apart relation on the opposite sides of the switch operating member 82 is a pair of identical snap-acting switch devices 87 and 88 which may be of any suitable commercially available type.

The snap-acting switch devices 87 and 88 are identical in construction. Therefore, a description of one will suflice for both, it being understood that corresponding parts of the switch device 88 have the same reference numerals as those of the switch device 87.

The switch device 87 is provided with an operating arm 89 that, as shown in the FIGURE, is provided on its left-hand end with a clevis 90 in the opposite jaws of which is anchored the opposite ends of a pin 91. Rotatably mounted on the pin 91 between the jaws of the clevis 90 is a roller 92 which, when the switch operating member 82 is shifted in the direction of the right-hand in a manner hereinafter explained, rides or rolls up the upper inclined surface at the left-hand end of the groove 86 to efiect rocking of the operating arm 89 clockwise about a pin 93 on which this arm 89 is pivotally mounted adjacent its right-hand end, as shown in the FIGURE. The design of the switch device 87 is such that when the vertical movement of the roller 92, as it rides up the inclined surface at the left-hand end of the groove 86, is, for example, a minimum of 0.l25- inch, the arm 89 is rocked clockwise about the pin 93 through an angle sufficient to effect closing of a pair of contacts of this switch device and thereby establishing a circuit to control operation of any suitable electrical device.

The switch device 88 is secured to the other leg of the angle bracket 77 in such a position that its roller 92 is disposed on the opposite side of the switch-operating member 82 from the roller 92 of the switch device 87 and at the opposite end of the groove 86. Consequently, when the switch operating member 82 is shifted in the direction of the left-hand, in a manner hereinafter explained, the roller 92 of the switch device 88 rides down the lower inclined surface at the right-hand end of the groove 86 to effect counterclockwise rocking of the operating arm 89 of this switch device 88 about the corresponding pin 93 to effect closing of the corresponding switch contacts and thereby establishing a circuit to control operation of any suitable electrical device.

Referring to the drawing, it will be seen that the casing section 26 is provided with a bore which at one end opens into the chamber 29 and at its opposite end opens into a coaxial counterbore 101 at the wall surface of which opens one end of a passageway 102 that is fonned in the casing section 26. This passageway 102 extends in spaced relation arcuately around the counterbore 75 in the casing section 26 and at its opposite end opens into the hereinbefore-mentioned passageway 33 intermediate the ends thereof.

It will be further noted from the FIGURE that a bushing 103 is press-fitted into the bore 100 and that a plunger 104 is slidably mounted in this bushing. Furthermore, it will be noted that the casing section 26 is provided with two counterbores 105 and 106 that are also coaxial with the bore 100, and that an annular member 107 having an annular valve seat 108 formed at its right-hand end is press-fitted into the counterbore 105. The right-hand end of the counterbore 106 is closed by a cup-shaped cylindrical spring seat member 109 having a peripheral annular groove in which is disposed an O-ring 110 that forms a seal with the wall surface of the counterbore 106 to prevent flow of fluid under pressure from the interior thereof to atmosphere.

Disposed within the cup-shaped cylindrical spring seat member 109 is a flat disc-type valve 111 between which and the spring seat 109 is interposed a spring 112 which is normally effective to bias the valve 111 against its seat 108 to close communication between the passageway 102 that opens into the counterbore 101 and a passageway 113 in the casing section 26 opening at one end at the wall surface of the counterbore 106 and having connected to its opposite end a correspondingly numbered pipe through which fluid under pressure may be supplied to the interior of the counterbore 106.

Assume that fluid under pressure is supplied to the chamber 28 in the master controller switch device 9, via the pipe and passageway 30. Accordingly, it is apparent that this fluid under pressure is effective to deflect the diaphragm 27 in the direction of the right-hand, as viewed in the FIGURE, against the yielding resistance of the spring 71. This deflection of the diaphragm 27 in the direction of the right-hand is effective to shift the stem 36 and switch operating member 82 in the same direction.

it is apparent from the FIGURE that, as'the switch operating member 82 is shifted in the direction of the right-hand, the roller 92 of the snap-acting switch device 87 rides or rolls up the upper inclined surface at the left-hand end of the groove 86 to effect clockwise rocking of the arm 89 of this switch device about the corresponding pin 93. As hereinbefore stated, when the vertical movement or lift of this roller 92 reaches a value of, for example, 0. l 25-inch, the corresponding clockwise rocking of the arm 89 effects closing with a snap action the contacts of this switch device 87. When these contacts are thus closed, the circuit to the electrical device controlled by the switch device 87 is established.

It may be assumed that operation of the device controlled by the switch device 87 caused fluid under pressure to be supplied to the chamber 29 in the master controller self-lapping switch device 9 via the pipe and corresponding passageway 33. Fluid under pressure thus supplied to the chamber 29 rapidly increases the pressure in this chamber and is effectively to establish a force that acts in a left-hand direction on the right-hand side of the diaphragm 27. Upon this force slightly exceeding the force acting on the left-hand side of the diaphragm 27 as a result of the fluid under pressure previously supplied to the chamber 28 via the pipe and passageway 30, the diaphragm 27 will be deflected in the direction of the lefthand until the stem 36 and switch operating member 82 which are moved therewith are returned to the position in which they are shown in the FIGURE.

As the switch operating member 82 is moved in the direction of the left-hand to the position shown in the FIGURE, the roller 92 of the snap-acting switch device 87 rides down the upper inclined surface at the left-hand end of the groove 86 until it reaches the position shown. As the roller 92 of the switch device 87 returns to the position shown, the arm 89 of this switch device rocks counterclockwise about the corresponding pin 93 to effect opening with a snap action the contacts of this switch device thus opening the circuit to the electrical device controlled thereby.

It should be noted that in the above-described operation of the master controller switch device 9, the deflection of the diaphragm 27 of this switch device in the direction of the right-hand is not sufficient for the diaphragm follower 38 to contact the left-hand end of the plunger 104 and thereafter shift this plunger'in the direction of the right-hand to effect unseating of the valve 111 from its seat 108.

Assume that now fluid under pressure is released from the chamber 28 of the master controller switch device 9 via the pipe and passageway 30. Accordingly, the higher pressure present in the chamber 29 will deflect the diaphragm 27 in the direction of the left-hand, as viewed in the FIGURE against the yielding resistance of the spring 70. This deflection of the diaphragm 27 in the direction of the left-hand, is effective to shift the stem 36 and switch operating member 82 in the same direction.

It can be seen from the FIGURE that, as the member 82 is shifted in the direction of the left-hand, the roller 92 of the snap-acting switch device 88 rides or rolls down the lower inclined surface at the right-hand end of the groove 86 to effect counterclockwise rocking of the arm 89 of this switch device about the corresponding pin 93. When the vertical downward movement of this roller 92 reaches a value of, for example 0. l25-inch, the corresponding counterclockwise rocking of the arm 89 effects closing with a snap-action the contacts of this switch device 88. When these contacts are thus closed, the circuit to the electrical device controlled by the switch device 88 is established.

It may be assumed that the switch device 88, when its contacts are closed, effects operation of electropneumatic devices (not shown) that cause a rapid reduction in the pressure of fluid in the chamber 29 until the pressure in this chamber is reduced to a value slightly below the reduced pressure present in the chamber 28. Upon the fluid pressure force acting on the right-hand side of the diaphragm 27 thus becoming slightly less than the fluid pressure force acting on the left-hand side of this diaphragm as the result of venting fluid under pressure from the chamber 29 to atmosphere via the above mentioned electropneumatic devices, the diaphragm 27 will be deflected in the direction of the right-hand to the position shown in the FIGURE and the switch-operating member 82 will likewise be moved in the direction of the right-hand to the position in which it is shown.

As the switch operating member 82 is moved in the direction of the right hand to the position shown in the drawing, the roller 92 of the snap-acting switch device 88 rides up the lower inclined surface at the right-hand end of the groove 86 until it reaches the position shown in the drawing. As this roller 92 returns to the position shown in the drawing, the arm 89 of the switch device 88 rocks clockwise about the corresponding pin 93 to effect opening with a snap action the contacts of this switch device thereby opening the circuit to the electrical device controlled thereby whereupon the electropneumatic devices controlled by this switch 88 operate to terminate venting of fluid under pressure from the chamber 29 in the master controller switch device 9 to atmosphere.

Therefore, it is apparent from the foregoing that the master controller switch device 9 operates in response to a reduction of pressure in its chamber 28 to cause a corresponding reduction in the pressure in the chamber 29.

It should be noted that in the above-described operation of the master controller switch device 9, the deflection of the diaphragm 27 in the direction of the left-hand is not sufficient for the stem 45 to contact the right-hand side of the valve 57 and thereafter unseat this valve from its seat 56. Accordingly, so long as the snap-acting switch devices 87 and 88 operate properly and there is no break or short in the circuits controlled by these switch devices, the valves 57 and 111 are not unseated from their respective seats 56 and 108.

Let it now be supposed that, due to a short circuit or malfunctioning of the switch device 87, no electrical current is supplied to the electropneumatic devices controlled thereby when fluid under pressure is supplied to the chamber 28 in the master controller switch device 9. Accordingly, these do not operate to supply fluid under pressure to the chamber 29 in the switch device 9 to increase the pressure therein. Therefore, the fluid under pressure being supplied to the chamber 28 in the manner described above is effective to deflect the diaphragm 27 in the direction of the right-hand until the diaphragm follower 38 abuts the left-hand of the plunger 104. The continued supply of fluid under pressure to the chamber 28 deflects the diaphragm 27 further in the direction of the right-hand to effect shifting of the plunger 104 in this direction which unseats valve 111 against the yielding resistance of spring 112 from valve seat 108. If it is assumed that fluid under pressure is present in the passageway and pipe 113, it will flow past the now unseated valve 111 and to the chamber 29 via counterbore I01, passageway I02, and passageway and corresponding pipe 33. Fluid under pressure will thus flow to the chamber 29 until the pressure therein is substantially equal to that in the chamber 28 whereupon the diaphragm 27 will be deflected in the direction of the left-hand until the spring 112 seats valve 111 on the seat I08 to cut off further flow of fluid under pressure from the pipe and passageway 113 to the chamber 29.

From the foregoing it is apparent that the master controller switch device 9 embodies therein a fail-safe feature in that the passageway and pipe 33 are charged to substantially the same pressure as the passageway and pipe 113 notwithstanding an electrical failure of the snap-acting switch device 87 or the circuit controlled thereby.

It will be apparent from the FIGURE that if the snap-acting switch device 88 becomes inoperative or a short occurs in the circuit controlled thereby so that the electropneumatic devices controlled thereby are not energized to cause these devices to vent fluid under pressure from the chamber 29 in the master controller device 9, the reduction in pressure in the chamber 28 of the master controller device 9 enables the pressure present in the chamber 29 to deflect the diaphragm 27 in direction of the left-hand until the stem 45 unseats valve 57 against the yielding resistance of spring 69 from its seat 56.

If it is assumed that the pipe 58 is connected to the pipe 33 which is connected by the correspondingly numbered passageway to the chamber 29 in the master controller switch device 9, fluid under pressure will flow from the chamber 29 to atmosphere via the now unseated valve 57, interior of member 55, counterbore 43, and passageway and pipe 5 ft Fluid under pressure will thusTbT vented from the chamber 29 until the pressure therein is substantially equal to that in the chamber 28 whereupon the diaphragm 27 will be deflected in the direction of the right-hand until the spring 69 seats valve 57 on its seat 56 to cut off further flow of fluid under pressure from the chamber 29 to atmosphere.

' From the foregoing it will be seen that the fail-safe feature of the master controller switch device 9 also insures a reduction in the pressure in the chamber 29 notwithstanding malfunctioning of the snap-acting switch device 88 or a short in the circuit controlled hereby.

We claim:

1. A fluid pressure operated switch device comprising:

a. a movable abutment subject in opposing relation to a first pressure in one chamber at one side thereof and to a second pressure in a second chamber at the opposite side, said abutment being shifted in opposite directions respectively from a neutral position accordingly as the pressure in one of said chambers exceeds the pressure in the other of said chambers;

b. an operating rod secured at one end to said abutment for movement therewith and having formed thereon adjacent its opposite end two spaced-apart inclined cam surfaces;

c. one switch means having an operating member disposed in contacting relation to one of said inclined cam surfaces so that said switch means is operated from an open position to a closed position upon shifting of said abutment out of its neutral position in one direction a distance less than that required to cause said operating member to travel the length of said one inclined cam surface;

d. another switch means having an operating member disposed in contacting relation to the other of said inclined cam surfaces so that said another switch means is operated from an open position to a closed position upon shifting of said abutment out of its neutral position in an opposite direction a distance less than that required to cause said operating member to travel the length of said other of said inclined cam surfaces; wherein the improvement comprises; and

e. a first valve means operated, upon shifting of said abutment in said one direction out of the neutral position thereof a distance greater than that required to effect closing of said one switch means, to establish a communication via which to introduce into said one chamber fluid under pressure for restoring-a balance of fluid pressure forces on said abutment to effect restoration thereof to neutral position.

2. A switch device, as recited in claim 1 further characterized by a second valve means operated, upon shifting of said abutment in said opposite direction out of the neutral position thereof a distance greater than that required to effect closing of said another switch means, to establish a communication via which to release fluid under pressure from said second chamber to restore a balance of fluid pressure forces on said abutment to effect restoration thereof to its neutral position. 

1. A fluid pressure operated switch device comprising: a. a movable abutment subject in opposing relation to a first pressure in one chamber at one side thereof and to a second pressure in a second chamber at the opposite side, said abutment being shifted in opposite directions respectively from a neutral position accordingly as the pressure in one of said chambers exceeds the pressure in the other of said chambers; b. an operating rod secured at one end to said abutment for movement therewith and having formed thereon adjacent its opposite end two spaced-apart inclined cam surfaces; c. one switch means having an operating member disposed in contacting relation to one of said inclined cam surfaces so that said switch means is operated from an open position to a closed position upon shifting of said abutment out of its neutral position in one direction a distance less than that required to cause said operating member to travel the length of said one inclined cam surface; d. another switch means having an operating member disposed in contacting relation to the other of said inclined cam surfaces so that said another switch means is operated from an open position to a closed position upon shifting of said abutment out of its neutral position in an opposite direction a distance less than that required to cause said operating member to travel the length of said other of said inclined cam surfaces; wherein the improvement comprises; and e. a first valve means operated, upon shifting of said abutment in said one direction out of the neutral position thereof a distance greater than that required to effect closing of said one switch means, to establish a communication via which to introduce into said one chamber fluid under pressure for restoring a balance of fluid pressure forces on said abutment to effect restoration thereof to neutral position.
 2. A switch device, as recited in claim 1 further characterized by a second valve means operated, upon shifting of said abutment in said opposite direction out of the neutral position thereof a distance greater than that required to effect closing of said another switch means, to establish a communication via which to release fluid under pressure from said second chamber to restore a balance of fluid pressure forces on said abutment to effect restoration thereof to its neutral position. 